License plate lights

Hi all;
I'm hoping you can help me....I have a 99 Chevy Blazer and recentlyl I tried to tow my boat with it. When I hooked up the lights, the running lights wouldn't come on. I assumed the problem to be with the trailer, so I checked all the connections, made sure it was grounded properly, ect. I then did some experimenting and noticed that the turn signal and brake lights work, but the running lights don't work. Again, I checked all wires, fuses, ect.....everything seemed to check out. I then tried the same thing with another trailer; again, the brake lights and turn signals work, but the running lights won't work. I was confused and then noticed that the lights around the license plate (not sure of the technical term for them) are out.....I checked in my owners manual, but there is no description as to how to change these bulbs. Is this something I can do myself, or do I have to take it to a mechanic or dealer? (Please let it be something I can fix myself....please!) If it is something I can do myself, how do I gain access to those bulbs? Thanks in advance

yes you can do it your self. I believe all it is, is you get under your truck and they should just twist out, then you pull the bulb out. Its really easy.